I imagine the most problematic abort in something like a NY to London flight would be if multiple engines fail several hundred miles out. All kinds of velocity in the wrong direction if you want to fly back, not enough thrust to maintain the proper trajectory towards the target. I think there are bound to be some scenarios where you can do a limping, powered landing (the vehicle probably only needs one or two working engines) but you have to do it downrange.
Aborts also leave you with too much fuel on board, probably way too much fuel. You could burn it off with the engines, although you'd want to actually use it to reach your origin or destination if possible.
If you abort early, you can still reach the origin. If you abort late, you can still reach the destination on the remaining engines. So the pertinent question is: do these two regimes overlap, or is there a gap, and how big? I don't have the answers, and you may be right that there is one.